Mobilization of Cd from human serum albumin by small molecular weight thiols

• LC was applied to study the stability of a Cd–human serum albumin (HSA) complex.
• Cd–HSA complex was injected on SEC column and Cd was detected in effluent.
• Effect of small molecular weight thiols in mobile phase on Cd-elution investigated.
• At 1.0 mM in mobile phase Cys and GSH were more effective than NAC in mobilizing Cd.
• Detected Cd–Cys and Cd–GSH complexes may be uptaken by mammalian target organs.

Although the toxic metal Cd is an established human nephrotoxin, little is known about the role that interactions with plasma constitutents play in determining its mammalian target organs. To gain insight, a Cd–human serum albumin (HSA) complex was analyzed on a system consisting of size exclusion chromatography (SEC) coupled on-line to a flame atomic absorption spectrometer (FAAS). Using phosphate buffered saline (pH 7.4) as the mobile phase, we investigated the effect of 1–10 mM oxidized glutathione (GSSG), l-cysteine (Cys), l-glutathione (GSH), or N-acetyl-l-cysteine (NAC) on the elution of Cd. As expected, GSSG did not mobilize Cd from the Cd–HSA complex up to a concentration of 4 mM. With 1.0 mM NAC, ∼30% of the injected Cd–HSA complex eluted as such, while the mobilized Cd was lost on the column. With 1.0 mM of Cys or GSH, no parent Cd–HSA complex was detected and 88% and 82% of the protein bound Cd eluted close to the elution volume, likely in form of Cd(Cys)2 and a Cd–GSH 1:1 complex. Interestingly, with GSH and NAC concentrations >4.0 mM, a Cd double peak was detected, which was rationalized in terms of the elution of a polynuclear Cd complex baseline-separated from a mononuclear Cd complex. In contrast, mobile phases which contained Cys concentrations ≥2 mM resulted in the detection of only a single Cd peak, probably Cd(Cys)4. Our results establish SEC–FAAS as a viable tool to probe the mobilization of Cd from binding sites on plasma proteins at near physiological conditions. The detected complexes between Cd and Cys or GSH may be involved in the translocation of Cd to mammalian target organs.